This invention is concerned with actinic light curable compositions which, when cured, are frangible. By this is meant that such cured compositions retain their coherency, physical integrity, and shape, resist disintgration and retain their original, general properties, they are capable of being easily cut, comminuted, dissected, excavated, or otherwise caused to lose their physical shape and integrity when desired. This invention deals with materials which are suited to applications where a form or cavity is filled on a temporary basis to seal it against the ingress of water, fluids, bacteria and the like. Such materials are particularly useful in dental, endodontic, and other medical, dental and industrial applications where it is desired to provide a reasonably hard, easily formed, and quickly hardenable shaped mass of material which can be removed from a dental space after curing without excessive difficulty or substantial trauma. Exemplary of these uses are "temporary fillings" for dental cavities and removable endodontic fillings.
Materials which are suitable for the temporary restoration of excavated carious lesions, voids or other cavities in teeth have been known heretofore. Such restorations, colloquially known as "temporary fillings", are indicated in many situations where permanent filling or restoration of a tooth is not called for. Materials useful for such purposes must be capable of firmly filling a prepared tooth space, such as an excavated cavity, without substantial leakage and with reasonable hardness while at the same time being capable of being removed as necessary either in whole or in part without substantial additional trauma to the tooth involved.
In endodontics, it is frequently necessary to provide repeated access to the pulpal space of a diseased, dead or dying tooth. In this regard, the pulpal space of such a tooth is excavated by the endodontic practitioner using a conventional array of tools. The diseased portions of the tooth are removed and the spaces cleaned of debris and detritus. Typically, the space is then medicated in order to suppress any remaining infection, to soothe the traumatized tissue, or otherwise to improve the endodontic environment. For this purpose, medicated paper "points", treated cotton pledgets or other forms of medicament are conventionally inserted into the excavated endodontic space, left for a period of time, usually a few days, and then removed. Such treatment may be repeated several times during the course of the endodontic protocol. It is obviously necessary to seal the pulpal space from the oral environment during these periods of medication or other treatment. For this purpose, the pulpal space is, ideally, filled towards its external portion with a material which is sufficiently strong and coherent to isolate the space from the oral environment, but which can, subsequently, be removed without substantial additional trauma being inflicted upon the tooth.
Dental spaces have been temporarily sealed heretofore by formulations of zinc oxide and eugenol. One such material is IRM.sup.R, a trademark of the L.D. Caulk division of Dentsply International Inc., assignee of this invention. IRM.sup.R is a polymer reinforced zinc oxide-eugenol which requires considerable time to harden. While adequate, such simple mixtures of zinc oxide and eugenol have not shown exceptional utility for this purpose since they are not particularly strong, are difficult to mix and manipulate, and tend to leak about the cavity margin.
Traditional dental restorative compositions have also been used heretofore in these roles. Their removal, however, is generally difficult, since these materials have been formulated to exhibit great strengths and to resist removal from a cavity and disintegrative forces. One such traditional restorative is PRISMA FIL.sup.R, a product of the L. D. Caulk division of Dentsply International Inc., assignee of the present invention. PRISMA FIL.sup.R is a visible light curable dental restorative generally described in U.S. Pat. No. 4,491,453--Koblitz et. al. Other restorative compositions, including other actinic light curable restorative compositions, have been known heretofore.
Another presently available material, CAVIT (a trademark of the Espe Company), has been offered for temporary endodontic sealing. This material, which is believed to comprise a polyvinyl acetate-based formulation believed to contain calcium sulfate hemihydrate, is water sorptive and has a tendency to leak fluids into the pulpal space--a decidedly undesirable effect. This material hardens very slowly requiring uptake of moisture.
It is greatly desired to provide materials which are coherent and reasonably strong, which harden upon command and which do not leak, but which are capable of being removed easily when desired.
See in this regard "The Leakage of Materials Used As Endodontic Dressing Seals", TYDSKRIF Van Die T.V.S.A.--Valcke et al June 1978, incorporated herein by reference.